Julien Jarrige

Finite element analysis of ring-shaped emission profile in plasma bullet

In this study, we focus on the mechanisms of ring-shaped emission patterns observed in a plasma bullet.1: Our model is based on a fluid model with the local field approximation in ID cylindrical coordinates, corresponding to a cross-section of a plasma bullet. An expected concentration gradient of humid air is assumed to be present due to diffusion of air into helium gas flow. The current model is almost identical to our previous report2. The major difference is that uniform pulselike electric field is given perpendicular to the simulation domain. The pulse width and repetition rate are determined based on experimental conditions. The magnitude of the electric field was chosen so that a periodic steady state solution can be obtained. We also performed spectroscopic measurements to investigate the structure of the plasma bullets and to compare with the simulation results. Figure 1 shows comparison of spatially-resolved emission profiles from nitrogen second positive systems between experiment and simulation. Light emission from nitrogen clearly shows an off-centered peak (ring-shaped profile) in both experiment and simulation. Our simulation results indicate that diffusion of air (nitrogen) into the helium flow plays a key role. Penning ionization between helium metastables and nitrogen generate the ring-shaped emission profile.

Electron dynamics and ion acceleration in expanding-plasma thrusters

In most expanding-plasma thrusters, ion acceleration occurs due to the formation of ambipolar-type electric fields; a process that depends strongly on the electron dynamics of the discharge. The electron properties also determine the heat flux leaving the thruster as well as the maximum ion energy, which are important parameters for the evaluation of thruster performance. Here we perform an experimental and theoretical investigation with both magnetized, and unmagnetized, low-pressure thrusters to explicitly determine the relationship between the ion energy, E i , and the electron temperature, T e0. With no magnetic field a relatively constant value of is found for xenon, while when a magnetic nozzle is present, is between about 4–5. These values are shown to be a function of both the magnetic field strength, as well as the electron energy distribution function, which changes significantly depending on the mass flow rate (and hence neutral gas pressure) used in the thruster. The relationship between the ion energy and electron temperature allows estimates to be made for polytropic indices of use in a number of fluid models, as well as estimates of the upper limits to the performance of these types of systems, which for xenon and argon result in maximum specific impulses of about 2500 s and 4500 s respectively.

Characterization of a coaxial ECR plasma thruster

The Electron Cyclotron Resonance (ECR) plasma thruster is an electric propulsion device that combines the high ionization performances of an ECR source and the simultaneous acceleration of electrons and ions in a magnetic nozzle. A coaxial ECR thruster under development at ONERA is tested using xenon as the propellant gas. The influence of mass flow rate and microwave power on ion current and ion energy distribution is evaluated. Mass utilization efficency up to 45% and ion energy up to 350 eV have been obtained with a microwave power around 50 W.